FM Transmitter circuit

FM transmitter having a stable frequency & with a high power (Range) is a tough task to do , actually you can buy a high power FM transmitter , but hard to make it due to the restriction as well as parts availability in the certain areas , in my this circuit the input were taken from the Car MP3 modulator , antenna point at the PCB can be easily found , where they always printed the every point on the PCB , if not found the antenna point then you can use the field strength  meter  (FSM) , antenna will be the peak FSM reading , this signal were then given to the circuit , sometime the RF power from the MP3 found low which cannot derive the  first transistor , for this biasing required from positive supply to the transistor base to boost some hove the input signal , 30 k to 56 k resistor can be used for the biasing ,in first stage I used 2sc2407 transistor ,in the other next stages both 2sc3950 were used , very cheap transistors ,where all these transistor can work very nice in the FM range, RFC were used at the transistor collector which can be easily available in the market  RFC for FM rage will be 0.56 mh  or 0.68 mh (Micro henry)  you don’t have to wound the coil , you can use 2N2219 , 2N3866, 2N2222 instead 2sc2407 , instead of 2sc3905 , you can use 2sc1971 , 2n3553 etc.

  

FM Transmitter 1 Watt ( 88 MHz - 108 MHz)

Simple 2-Transistor High-Power FM Transmitter (2SC2407 & 2SC3950)

Building a stable, high-power FM transmitter from scratch can often be challenging due to component availability and frequency drift. However, this simple 2-transistor circuit offers a reliable, low-cost solution using easily accessible parts.

Circuit Highlights & Transistor Lineup

• First Stage (Driver): Uses the 2SC2407 transistor (Alternative options: 2N2219, 2N3866, or 2N2222 can also be used).

• Final Stage (Power Amplifier): Uses the 2SC3950 power transistor (Alternative options: 2SC1971 or 2N353).

• Tuning & Inductors: Uses readily available RF Chokes (RFC) for the transistor collectors—specifically 0.56 $\mu$H or 0.68 $\mu$H—eliminating the need to hand-wind complex coils. A 2–30 pF variable capacitor (or a fixed 20 pF capacitor) is used for tuning.

Audio Input & Biasing Tips

• Source: The audio/RF input is taken directly from a Car MP3 Modulator.

• Input Boosting: If the RF output power from the MP3 modulator is too weak to properly drive the first transistor stage, you can add forward biasing. Connect a 30k to 56k resistor from the positive supply rail to the transistor base to boost the incoming signal level.

Antenna Tuning Guide

• PCB Labels: The antenna connection point is usually clearly printed on the PCB layout.

• Using an FSM: If the antenna point is not marked, you can use a Field Strength Meter (FSM). Adjust your circuit until you achieve the peak FSM reading to ensure maximum RF power transfer to the antenna.